The present invention relates to multicylinder internal combustion engines including exhaust gas treatment devices wherein certain of the cylinders is deactivated in response to a sensed engine power demand when reduced engine power can adequately operate the vehicle.
Variable cylinder disablement is known in the art as an effective means to improve fuel economy by selectively shutting off fuel supply to several cylinders of the engine when reduced power output can operate the vehicle adequately. This disablement, known as variable displacement control, is particularly advantageous for application to electronic fuel injection because the fuel injectors can be electronically disabled to cut off fuel without having the need for mechanical parts to shut off intake valves as would be required in carbureted engines. However, the combined use of variable displacement control with exhaust gas treatment devices such as catalytic converters or thermal reactors would accompany disadvantages in the operation of such devices since the disabled cylinders draw in air which consequently increase the amount of air in the exhaust system so that the temperature of the exhaust gases tends to drop below the normal operating range of the gas treating device.